2012/12/28

I recently acquired this pair of Ward Beck M480 input modules. Ward Beck Systems, or WBS, have a great reputation, and so I am very keen to get these racked up as microphone preamps. The modules have four switchable inputs, and a parametric EQ section too.

I have not yet found a copy of the M480 manual, but the Ward Beck Preservation Society have the manual for the later variant, M480C. The pin assignments look the same although the later 'C' revision has some additional features such as a switchable phantom.

The modules are very neat and clean inside, and use 44 pole PCB edge connectors. Luckily I had three gold plated connectors in the parts bin. These were salvaged from some scientific equipment that I pulled from a skip. It pays to recycle... and never throw anything away!

Although the modules are in great shape inside, the front panels and knobs are very dirty from years of sticky fingers. Naughty engineers!

The collet knobs can be removed by popping off the coloured caps, and then loosening the central locking nut. Then the black control panel can be prised away from its glue. In both cases they are destined for a long zap in the ultrasonic bath, which will clean them up nicely.

WBS M480 stripped down for racking

The modules will be mounted in a standard 19 inch rackmount case, and the construction makes this very simple. The existing aluminium front plates can be used as templates to drill the holes in the new front panel, and the black screen printed control panels can be mounted over these. Then it just needs a ±24V power supply and we will be ready to go.

2012/12/20

Here is an old Ferrograph brochure whoch arrived with a Reslo ribbon microphone. Built like tanks, Ferrograph made arguably the best reel to reel tap recorders through the 50s and 60s, and it seems that they had a formal agreement with Reslosound as the two names often appear together in catalogs. The final page of the document shows the Reslo RB microphone, along with accessories including matching transformers and stands.

The Reslo microphone sold for 11 Guineas at the time of publishing. (1 Guinea = one pound and one shilling. Only the British could come up with such a bizarre coin!)

2012/12/18

One challenge when building prototype pickups is testing them quickly. It is easy enough to make the electrical measurements such as inductance, resistance and capacitance, but they don't really tell you how the pickup is actually going to sound. Sooner or later they need to go into a guitar.

Squier by Fender Jagmaster ready for surgery

Changing a guitar pickup isn't a big job, but it still takes time. Usually the strings need to come off, the scratch plate removed, a bit of soldering, and then back together again before tuning. If you add a cup of tea then you can easily lose an hour.

So I wanted to make or modify a guitar to act as a workhorse for pickup testing, which would allow for quick pickup swaps without having to take the strings off. The obvious approach is to put the pickups in from the rear of the guitar - which means cutting a hole through a guitar and finding an alternative way to mount the pickup.

This Squier Jagmaster guitar makes a suitable victim for surgery. It was fairly cheap, the neck is straight and plays well, and the strat-style trem cutout means that I don't need to remove a huge amount of wood.

The first job it to strip the Jagmaster down, removing the strings, scratch plate and the existing hardware from the front of the guitar, and the tremolo system from the rear. Then off with the neck to keep it safely out of the way when the jigsaw comes to play.

Once everything is out then I measured up and cut two aluminium rails that will act as mounts for the new pickups. These were filed round at the ends to fit the existing routing, and drilled and tapped for mounting.

Then came the dirty work. With a jigsaw I cut through the body to make a humbucker-sized hole. You can see just how thin the wood is between the pickup and the tremolo routings - just a few millimetres.

After the jigsawing, the hole was cleaned up with a wood file. The rails were then screwed into the body at the top of the guitar - the holes countersunk so that they don't get in the way of the pickups.

One more job - the bridge no longer has springs to keep it under tension. A block of wood locks it in place instead. The guitar can now be put back together.

Now the pickup can be fitted from the rear with two screws attaching it to the aluminium rails. Screw terminals are also used to connect the wires to the output sockets for the ultimate quick change experience. A brass plate will cover the mess.

Rear of 'quick change' Jagmaster with locked tremolo and pickup mount

Now it takes two minutes to swap a pickup! Time for some rapid prototyping. And here's the front of the guitar with a hexapup fitted from the rear.

2012/12/16

Lustraphone was one of several British companies making microphones back in the 50s and 60s. The catalog includes product sheets for several microphones and also some accessories such as mic stands and matching transformers. I was lucky enough to come across some old Lustraphone catalog pages, which included a product sheet for the VR53 ribbon velocity microphone and several other microphones. The catalog probably dates from 1952 or 1953. Note the four digit phone number!

Lustraphone VR53 ribbon mic data sheet front

Lustraphone VR53 ribbon mic catalog, reverse

Although the catalog mentions 20 ohm and 500 ohm models, I have also seen high impedance models of this mic. The frequency response is claimed to be "substantially maintained to 14000 Hz". From experience, I would say that 'substantially' is used loosely. The BBC have a bit more to say about this mic in their R&D reports.